Analysis of the Effect of the Biomass Torrefaction Process on Selected Parameters of Dust Explosivity

Abstract

This article presents the findings of a study investigating the explosion and combustion parameters of dust from the raw biomass of wheat straw and energy willow and from the products of biomass torrefaction generated at temperatures ranging from 220 to 300 °C. Agricultural waste and energy crops and their modifications, e.g., in the torrefaction process, did not find a place in explosive risk research, which the authors decided to present in their work. The study was designed to estimate explosion hazard during the processing of the materials into fuels and during the storage process. The measurements recorded a maximum explosion pressure Pmax in the case of dust from biomass ranging from 7.2 to 7.3 bar and for dust from torrefied materials amounting to 7.5–9.2 bar, and a maximum rate of pressure rise over time (dp/dt)max in raw biomass ranging from 201.4 to 261.3 bar/s and in torrefied materials amounting to 209.6–296.6 bar/s. The estimated explosion index Kstmax for raw biomass was 55–72 m*bar/s and for torrefied materials was in the range from 57 to 81 m*bar/s. In the results, the authors present values for specific types of fuel which differ significantly depending on the type of biomass. The research findings show that the torrefaction process used in fuel production is not associated with a significantly greater risk of explosion and the materials obtained may safely be used as an alternative to conventional solid fuels. Given the growing interest in the use of biomass and in the variety of biomass processing methods for energy-related purposes, it seems there is a need for research to develop appropriate guidelines and for effective practices to be introduced in the energy industry in order to ensure the safety of the processes used in the production of novel fuels especially in small installations converting these materials into more efficient energy material.

Effect of the Pyrolysis Process Applied to Waste Branches Biomass from Fruit Trees on the Calorific Value of the Biochar and Dust Explosivity

“…Pyrolysis leads to higher carbon concentrations and volatile contents and results in the increased brittleness of the thermally processed products. A similar relationship was reported by Bajcar et al (2020), who assessed the dust explosivity in the raw biomass of wheat straw and energy willow and in products of the torrefaction process applied to those materials. The authors observed that Pmax increased by a maximum of 28% with a higher torrefaction process temperature [47].…”

“…A similar relationship was reported by Bajcar et al (2020), who assessed the dust explosivity in the raw biomass of wheat straw and energy willow and in products of the torrefaction process applied to those materials. The authors observed that Pmax increased by a maximum of 28% with a higher torrefaction process temperature [47]. Półka (2020) reported a maximum explosion pressure for coke dust amounting to 6.84 bar.…”

Oak Biomass in the Form of Wood, Bark, Brushwood, Leaves and Acorns in the Production Process of Multifunctional Biochar

“…Bajcar et al showed an increase in the explosion index K st max , which, in the case of raw willow biomass, was estimated at the level of 72 bar s −1 , and for the torrefied material amounted to 81 bar s −1 . A similar tendency was identified in the case of wheat straw; the dust explosion index K st max of raw biomass amounted to 55 bar s −1 , and with the torrefied materials it increased to 62 bar s −1 [ 143 ]. Saletnik et al classified the thermally unprocessed oak, coniferous pellets and their mixture, as well as the thermally processed forms obtained from them, into the first class of dust explosion hazard (St1)—a material not susceptible to explosiveness.…”

“…The thermal processes leads to an increased concentration of carbon, higher contents of volatile substances, and greater brittleness observed in the materials after thermal treatment. Despite the visible trend, these differences are not significant and do not result in a change of dust classification [ 143 ]. According to Cashdollar, Cordero et al and Demirbas, as well as other researchers, the differences between raw and thermally processed biomass can mainly be explained by the different emissivity of the respective materials linked to the mechanisms of heat transfer [ 145 , 146 , 147 ].…”

Overview of Health and Safety Risks in the Process of Production and Storage of Forest Biomass for Energy Purposes—A Review

“…During the production of wood chips, wood dust often swirls in cloud concentrations, which, especially in combination with fuel vapors and engine heat, can create a dangerous explosive mixture that can endanger the life and health of workers, as well as cause damage to property and equipment [90,91].…”